Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 343 AM EDT Sun Sep 15 2024 Valid 12Z Sun Sep 15 2024 - 12Z Tue Sep 17 2024 ...Heavy rain/flash flood threat continues today for portions of the Lower Mississippi Valley and Southeast... ...A coastal storm will bring wind and rain to the Carolinas and Mid-Atlantic over the next few days... ...A strong low pressure system will bring unsettled weather and well below normal temperatures to the West with high-elevation snow in the Sierra Nevada... Francine's remnants will linger over the southeastern U.S. early this week as a nearly stationary frontal boundary sags south to the Gulf Coast. Chances for locally heavy rain and isolated to scattered instances of flash flooding will continue today for portions of the Lower Mississippi Valley and Southeast. There is a Slight Risk of Excessive Rainfall (level 2/4) for parts of Mississippi, Alabama, and the Florida panhandle where flooding will be most likely. Chances for showers and storms will persist across this region over the next few days, but the risk of flooding will gradually decrease, with only isolated flooding concerns expected Monday and Tuesday. Meanwhile, a separate area of low pressure will strengthen off the Southeast Coast and gradually move north towards the Carolinas. This system is likely to bring gusty winds, heavy rain, coastal flooding, and dangerous beach conditions to the Carolinas and portions of the Mid-Atlantic through mid-week. Strong high pressure over the Northeast will slow the forward motion of this system, increasing the chance of heavy rainfall totals and flash flooding. There is a Slight Risk of Excessive Rainfall (level 2/4) for portions of the eastern Carolinas and far southeastern Virginia with an embedded Moderate Risk (level 3/4) over southeastern North Carolina where the risk of flash flooding will be highest. The National Hurricane Center is also monitoring this system for potential subtropical or tropical development, and has marked this area with a 50% chance of tropical formation over the next 48 hours. There is still quite a bit of uncertainty on the timing, intensity, and track of this system, so regularly check for forecast updates over the next couple of days. In the West, an unsettled pattern is beginning to take root as upper level troughing moves into the region. A deep upper low will move over the West Coast today and Monday and push across the Intermountain West to the Rockies on Tuesday. This will push a strong frontal system across the West that will bring widespread precipitation chances and much cooler temperatures to the region over the next few days. Precipitation will mainly fall as rain, but temperatures will be cold enough in the high elevations of the Sierra Nevada for some early season snow. A Winter Weather Advisory is in effect for portions of the Sierra Nevada above 8000 feet where up to 4 inches of snow may fall tonight and Monday. Precipitation chances will also increase across the Southwest/Four Corners region today as tropical moisture streams north from Tropical Cyclone Ileana, which will support monsoon-like showers and thunderstorms through Tuesday. Temperatures will have a large range across the United States over the next few days. Forecast precipitation and cloud cover will keep temperatures slightly below normal across the Southeast and Mid-Atlantic, with highs from the mid 70s to the mid 80s. Well above average temperatures are forecast for the Central U.S. and Northeast, with the highest anomalies forecast to develop under high pressure in the Upper Midwest/Great Lakes region. High temperatures will reach the 80s and 90s, which will be 10-20 degrees above normal for some areas. Well below average temperatures are forecast to spread across the West through Tuesday under the deep upper low/trough, and high temperatures will be as low as 15-25 degrees below normal. The coldest anomalies will be in Oregon, Nevada, and California on Monday. Highs in the 50s will be common in the Great Basin, and highs will likely only reach the 30s and 40s in the Sierra Nevada. Dolan Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php